Silicone elastomer material suitable for use in particular for making dental impressions

ABSTRACT

Described are methods for preparing organopolysiloxane compositions that are capable of cross-linking and/or of hardening by polyaddition reactions so as to produce elastomers or materials made of silicone. Further described, is how the methods are useful for making a dental impression in the context of preparing prostheses.

This application is a continuation of U.S. patent application Ser. No.13/993,970, filed Jun. 13, 2013, which is a U.S. National Stage ofPCT/FR2011/000644, filed Dec. 12, 2011, and designating the UnitedStates (published in French on Jun. 21, 2012, as WO 2012/080594 A1),which claims priority under 35 U.S.C. §119 to FR 1004844, filed Dec. 12,2010, each hereby expressly Incorporated by reference in its entiretyand each assigned to the assignee hereof.

The field of the present invention is that of organopolysiloxanecompositions suitable for crosslinking and/or curing by polyadditionreactions to form elastomers or silicone materials which are usefulespecially for the taking of dental impressions as part of theproduction of prostheses. These elastomers or silicone materials areused to take an intraoral impression for a dental prosthesis such as acrown, an inlay, or a dental device.

The expression “taking impressions” in the present specification isunderstood to define not only the operations of taking impressions of anarbitrary object and arbitrary shape in order to produce a model, moreparticularly a plaster model, but also the operations of reproducing orduplicating models made more particularly of plaster. The expression“taking of dental impressions” in the present specification is intendedto define not only the operations in which dental impressions are takenin the mouth in order to obtain exact reproductions of jaws or parts ofjaws that do or not carry, entirely or partly, teeth, and to formplaster models, but also the operations of duplicating in which modelsof jaws or parts of jaws are reproduced in plaster in a dentalprosthesis laboratory. The intended applications also encompass themanufacture of molded parts, other than duplicating compositions indental applications.

In the dental field, the use of elastomers or silicone materialsobtained by crosslinking and/or curing at room temperature, as a molduseful in the production of dentures, is continually growing. Theprecursor of this material is a composition having the consistency of apaste, into which a curing agent is introduced prior to use. Theresulting mass then looses its pasty consistency to take on a “rubbery”and elastic consistency in the course of curing at the temperature ofthe patient's body. By virtue of its elasticity, it is then easy toremove the cured silicone elastomer from the mouth, and it canthereafter be used to cast a working model from it, in plaster, forexample, from which the definitive denture is produced. The use ofsilicone elastomers is therefore widespread within the dental field.This is also due in part to the fact that the elastomers or siliconematerials offer on the one hand a great diversity of chemical,mechanical, and physical characteristics and, on the other hand, anontoxic, nonirritant, and nonallergenic character. Moreover, siliconematerials constitute poor growth substrates for microorganisms, and thisendows them with significant suitabilities with regard to hygiene.

Polyorganosiloxane compositions which crosslink by polyaddition aregenerally preferred within the dental impression sector since they allowelastomers or silicone materials to be obtained that are better qualityfrom the standpoint both of mechanical properties and of precision ofthe shapes reproduced. These compositions are sold in two separate partsrequiring mixing at the time of use, and are commonly referred to astwo-component compositions. In compositions of this kind, formulated intwo separate parts, one of the parts comprises at leastpolyorganosiloxane having per molecule at least two alkenyl groups eachbonded to a silicon atom, and a catalyst, which is generally a compoundof a metal from the platinum group, while the other part accommodates atleast one polyorganosiloxane having per molecule at least two hydrogenatoms bonded to a silicon atom. The polymerization, crosslinking, orcuring reaction of such compositions starts when the two parts aremixed—that is, the platinum-based catalyst, the polyorganosiloxanehaving per molecule at least two hydrogen atoms bonded to a siliconatom, and the polyorganosiloxane having per molecule at least twoalkenyl groups. The crosslinking rate varies according to the amounts ofcatalyst. The reactivity of the composition can also be adjusted byadding agents which inhibit or retard the polyaddition reaction. Thesecompounds are well known and act competitively with the catalyst,thereby retarding the crosslinking reaction.

After mixing of the two parts, the resulting composition begins to cureand the viscosity of the mixture increases; gelling (“gel setting”)starts until there is irreversible transformation into a crosslinkedpolymer or “elastomer”. When this gel setting point is reached, thecomposition flows with difficulty, and at a certain moment thecomposition can no longer be shaped by the user. Accordingly, a “workingperiod” or “working time” is defined within which the compositionremains able to be handled for an application such as the taking of adental impression. When the reaction is finished (or virtuallyfinished), the material or elastomer is said to have cured. This curetime is also an important parameter for a silicon impression material,since said material must remain in contact with the surface to bereplicated until it has completely cured. Within the field of dentalimpressions, the working time required is often of the order of severalminutes.

Accordingly, for applications which require the reproduction of details,such as the taking of a dental impression, the parameters of cure timeand working time must be controlled carefully. However, one of thefactors affecting both the working time and the cure time is theactivity of the catalyst. It is known that catalysts based on platinumare sensitive to long storage periods (a year or more), and this maygive rise to impairment of the crosslinking kinetics. This is manifestedin an increase in the cure time. This cure time becomes increasinglylong, and even unacceptable. The reason is that uncontrolled variationin the cure time jeopardizes the accuracy of an impression if the userwithdraws the silicone material from the model to be copied before saidmaterial has completely polymerized. What is worse, blackening phenomenaof the part comprising the platinum catalyst are also observed in thecourse of prolonged storage, making said part unusable.

Notably, this recurring problem has attracted a variety of approaches.For example, in U.S. Pat. Nos. 5,047,444, 5,118,559, and 5,182,316, thelevel of polymerization is controlled by detection of an ultravioletfluorophore which is generated during the polymerization. This approach,however, necessitates the installation of additional apparatus such as aUV radiation source and a UV fluorescence detector.

Patent application DE-19801657-A1 describes the preparation of aderivative obtained by reacting a selection of compounds (such asstarch, amylose, cellulose) with a platinum derivative in aqueous mediumfor 3 hours at preferably 60° C. Filtration and evaporation underreduced pressure gave a solid product with a yellow color and a Ptcontent of between 1% and 1.5% (see examples 1 and 2), which wasidentified as component (D). The starting products (for example, starch)were therefore removed by standard purification methods, and aretherefore no longer present in the additive prepared. Furthermore, thecompositions described are one-component compositions.

In a technical context of this kind, one of the essential objectives ofthe present invention is to overcome the problems encountered after longstorage (1 year or more) of two-component polyaddition compositionscatalyzed by a compound of a metal from the platinum group. The reasonis that these compositions then exhibit retardation of the kinetics ofthe polyaddition reaction, and this is manifested in an increase in theworking time and in a deterioration in the physical properties of theelastomer.

A second objective of the invention is to suppress the blackeningphenomena observed after long storage (1 year or more) of the partcomprising a catalyst, being a compound of a metal from the platinumgroup, of a two-component composition which crosslinks by polyadditionreactions.

In order to achieve this objective, among others, the inventors notablydiscovered, entirely surprisingly and unexpectedly, that the addition insufficient amounts of a specific additive, called a stabilizer in thepresent specification, allows the problems set out above to be overcome.

Accordingly, the present invention, as its first subject, provides acomposition X which is crosslinkable and/or curable by polyadditionreactions, taking the form of a two-component system S which comprisesat least two separate parts A and B intended for mixing to form saidcomposition X, and in which:

-   -   part A comprises:        -   (a) at least 25% by weight, relative to the total weight of            part A, of at least one stabilizer D selected from the group            of starches,        -   (b) at least one polyorganosiloxane V having per molecule at            least two alkenyl, preferably vinyl, groups which are each            bonded to a silicon atom,        -   (c) at least one catalyst C which is a compound of a metal            from the platinum group, and    -   part B comprises at least one polyorganosiloxane H having per        molecule at least two hydrogen atoms which are bonded to an        identical or different silicon atom.

The composition according to the invention has the advantage of beingstable on storage even under extreme conditions of temperature andhumidity. “Stable on storage” means that:

-   -   the kinetics of the polyaddition reaction catalyzed by the        platinum is unaffected by long storage, and    -   the suppression of the phenomenon of blackening of the part        containing the catalyst which is a compound of a metal from the        platinum group.

Starch is a carbohydrate macromolecule which is present in many plants,especially in the reservoir organs such as the potato tuber, and inseeds (wheat, corn, rice, etc.), where it constitutes a form of glucosestorage. In the starch molecule, glucose units connected by alpha 1-4glycosidic bonds form helicoidal amylose chains, on which short chainsof the same constitution branch off via alpha 1-6 glycosidic bonds. Instarch, these branches are present approximately every thirty glucoseresidues. In the presence of iodine, starch takes on a blue-violetcoloration.

The term “starch” also embraces so-called “modified” starches such as:

-   -   acid-treated starch;    -   base-treated starch;    -   bleached starch;    -   oxidized starch;    -   enzyme-treated starch;    -   monostarch phosphate;    -   glycerol starch;    -   distarch phosphate esterified with sodium trimetaphosphate;    -   phosphated distarch phosphate;    -   acetylated distarch phosphate;    -   starch acetate esterified with acetic anhydride;    -   starch acetate esterified with vinyl acetate;    -   acetylated distarch adipate;    -   acetylated distarch glycerol;    -   hydroxypropyl starch;    -   hydroxypropyl distarch phosphate;    -   hydroxypropyl distarch glycerol; and    -   sodium starch octenyl succinate.

According to one preferred embodiment, the stabilizer D is present atfrom 30% to 45% by weight, relative to the total weight of said part A.

With particular advantage, the stabilizer D is a corn starch.

The compound V is preferably a polyorganosiloxane having per molecule atleast two alkenyl groups bonded to silicon, and which comprises:

-   -   (a) at least two siloxyl units of formula:

$\begin{matrix}{T_{a}Z_{b}{SiO}_{\frac{4 - {({a + b})}}{2}}} & (1.1)\end{matrix}$

-   -   in which:        -   the symbols T are identical or different C₂-C₆ alkenyl            groups,        -   the symbols Z are identical or different monovalent            hydrocarbon groups selected from the group consisting of an            alkyl having 1 to 8 carbon atoms inclusive, optionally            substituted by at least one halogen atom, advantageously,            from the methyl, ethyl, propyl, and 3,3,3-trifluoropropyl            groups and an aryl, advantageously, from the xylyl, tolyl,            and phenyl radicals,        -   a is 1 or 2, b is 0, 1, or 2, and the sum a+b is 1, 2, or 3,            and    -   (b) optionally at least one siloxyl unit of formula:

$\begin{matrix}{Z_{c}{SiO}_{\frac{4 - c}{2}}} & (1.2)\end{matrix}$

-   -   in which:        -   the symbol Z has the same meaning as above and c is 0, 1, 2,            or 3.

The compound V is advantageously a polyorganosiloxane POS having aviscosity of between 10 and 200 000 mPa·s.

All of the viscosities referred to here correspond to a dynamicviscosity parameter which is measured, conventionally, at 25° C.

According to one particularly advantageous version, the composition Xaccording to the invention comprises at least two polyorganosiloxanes Vhaving per molecule at least two alkenyl groups each bonded to a siliconatom, preferably vinyl, and having dynamic viscosities ×1 and ×2 at 25°C. in the ranges 10 to 1000 mPa·s and from 1000 to 150 000 mPa·srespectively.

The polyorganosiloxane V may be solely formed of siloxyl units offormula (1.1) or may also contain siloxyl units of formula (1.2). It mayalso have a linear, branched, cyclic, or network structure.

Z is generally selected from methyl, ethyl, and phenyl radicals, andusually 60 mol % (or numerical percent) at least of the radicals Z aremethyl radicals.

Examples of siloxyl units of formula (1.1) are the vinyldimethylsiloxylunit, the vinylphenylmethylsiloxyl unit, the vinylmethylsiloxyl unit,and the vinylsiloxyl unit.

Examples of siloxyl units of formula (1.2) are SiO_(4/2) siloxyl,dimethylsiloxyl, trimethylsiloxyl, methylphenylsiloxyl, diphenylsiloxyl,methylsiloxyl, and phenylsiloxyl units.

Examples of polyorganosiloxane V are linear and cyclic compounds such asthe following: dimethylpolysiloxanes having dimethylvinylsilyl ends,(methylvinyl)-(dimethyl)polysiloxane copolymers having trimethylsilylends, (methylvinyl)-(dimethyl)polysiloxane copolymers havingdimethylvinylsilyl ends; and cyclic methylvinyl-polysiloxanes.

The catalyst C, which is a compound of a metal from the platinum group,is well known to the skilled person. Use may more particularly be madeof complexes of platinum with an organic product described in U.S. Pat.No. 3,159,601, U.S. Pat. No. 3,159,602, U.S. Pat. No. 3,220,972, andEuropean patents EP-A-0 057 459, EP-A-0 188 978, and EP-A-0 190 530; andthe platinum and vinyl organosiloxane complexes described in U.S. Pat.No. 3,419,593, U.S. Pat. No. 3,715,334, U.S. Pat. No. 3,377,432, andU.S. Pat. No. 3,814,730. The amount by weight of the catalyst C,calculated by weight of platinum metal, is generally between 2 and 400ppm, and preferably between 5 and 200 ppm, based on the total weight ofthe polyorganosiloxanes V and H.

The polyorganosiloxane H is a polyorganosiloxane which has per moleculeat least two hydrogen atoms bonded to the silicon, these Si—H groupsbeing situated within the chain and/or at the chain end.

According to one preferred version, when the polyorganosiloxane Vcontains 2 alkenyl groups per molecule, the polyorganosiloxane H will beselected so as to contain at least 3 hydrogen atoms bonded to thesilicon per molecule. Conversely, when the polyorganosiloxane H contains2 hydrogen atoms bonded to the silicon per molecule, thepolyorganosiloxane V will be selected so as to contain at least 3alkenyl groups per molecule.

The polyorganosiloxane H is more specifically a polyorganosiloxanecomprising:

-   -   (i) siloxyl units of formula:

$\begin{matrix}{H_{d}L_{e}{SiO}_{\frac{4 - {({d + e})}}{2}}} & (2.1)\end{matrix}$

-   -   in which:        -   L is a monovalent hydrocarbon group which has no unfavorable            effect on the activity of the catalyst and is preferably            selected from alkyl groups having 1 to 8 carbon atoms            inclusive, optionally substituted by at least one halogen            atom; advantageously, from methyl, ethyl, propyl, and            3,3,3-trifluoropropyl groups, and also from aryl groups, and            advantageously from xylyl, tolyl, and phenyl radicals,        -   d is 1 or 2, e is 0, 1, or 2, and the sum “d+e” is 0, 1, 2,            or 3,    -   (ii) and optionally other siloxyl units, of average formula:

$\begin{matrix}{L_{g}{SiO}_{\frac{4 - g}{2}}} & (2.2)\end{matrix}$

-   -   in which:        -   L has the same meaning as above and g is 0, 1, 2, or 3.

The dynamic viscosity of this polyorganosiloxane H is at least 10 mPa·sand is preferably between 20 and 1000 mPa·s.

The polyorganosiloxane H may be solely formed of siloxyl units offormula (2.1) or may additionally comprise siloxyl units of formula(2.2).

The polyorganosiloxane H may have a linear, branched, cyclic, or networkstructure.

The group L has the same meaning as the group Z described above.

Examples of siloxyl units of formula (2.1) are:

H(CH₃)₂SiO_(1/2),HCH₃SiO_(2/2),H(C₆H₅)SiO_(2/2)

The examples of units of formula (2.2) are the same as those givenearlier on above for the units of formula (1.2).

Examples of polyorganosiloxane H are linear and cyclic compounds such asthe following:

-   -   dimethylpolysiloxanes having hydrogenodimethylsilyl ends,    -   (dimethyl)(hydrogenomethyl)polysiloxane copolymers having        trimethylsilyl ends,    -   (dimethyl)(hydrogenomethyl)polysiloxane copolymers having        hydrogenodimethylsilyl ends,    -   hydrogenomethylpolysiloxanes having trimethylsilyl ends, and    -   cyclic hydrogenomethylpolysiloxanes.

The ratio of the number of hydrogen atoms bonded to the silicon in thepolyorganosiloxane H to the total number of groups with alkenylunsaturation in the polyorganosiloxane V is between 0.4 and 10,preferably between 1 and 5.

According to one particular embodiment, part A and/or part B comprisesat least one compound selected from the group consisting of thefollowing: a reinforcing filler Q1, a bulking filler Q2, a retarder orinhibitor I of polyaddition reactions, a polyorganosiloxane gum G havingper molecule at least two alkenyl, preferably vinyl, groups which arebonded to the silicon, and having a viscosity of greater than 1000 Pa·sat 25° C., a polydimethylsiloxane F used as diluent, a colorant K, aplasticizer P selected from the group consisting of liquid petroleumjelly and a paraffin, a wetting agent M, a silicone resin R, and abiocide N.

For the reinforcing filler Q1, the filler commonly used is a siliceousfiller. Siliceous fillers suitable for use include all precipitated orpyrogenic silicas (or fumed silicas) known to the skilled person. It isof course also possible to use mixtures of different silicas. Preferenceis given to precipitated silicas and/or fumed silicas having a BETspecific surface area of greater than 40 m²/g, and more specificallybetween 50 and 300 m²/g. More preferably, fumed silicas are used thathave the aforementioned specific surface area characteristics. Morepreferably still, fumed silicas are used that have a BET specificsurface area of between 100 and 300 m²/g. Generally speaking, thisreinforcing filler has an average particle size of less than 0.1 μm.

These silicas can be incorporated as they are or following treatmentwith organosilicon compounds commonly used for that purpose. Suchcompounds include methylpolysiloxanes such as hexamethyldisiloxane,octamethyldisiloxane, octamethylcyclotetrasiloxane, methylpolysilazanessuch as hexamethyldisilazane and hexamethylcyclotrisilazane,chlorosilanes such as dimethylchlorosilane, trimethylchlorosilane,methylvinyldichlorosilane, and dimethylvinylchlorosilane, andalkoxysilanes such as dimethyldimethoxysilane,dimethylvinylethoxysilane, and trimethylmethoxysilane. During suchtreatment the silicas may increase their initial weight to a level of20%, preferably 18% approximately. It is noteworthy that the particulatesiliceous mineral filler may advantageously be employed in the form ofthe suspension obtained by treating the filler by application of themethod in accordance with the teaching of patent applicationsWO-A-98/58997 and WO-A-00/00853, which envisage two-stage treatment ofthe filler with a compatibilizer (selected for example from: for thefirst treatment stage, a silazane, a hydroxy siloxane, an amine, or anorganic acid; and, for the second treatment stage, a silazane) andoperating in the presence of the POS constituent (1). Where suchtreatment leads to a basic pH, it is possible to add a neutralizingagent such as a weak acid, for example, to the dispersion. Suchparticular treatment of the filler is advantageous when it is necessaryto retain excellent fluidity for the silicone material (in thenoncrosslinked state). These fillers, when present, are added at from 2%to 30%, preferably even 3% to 20%, relative to the total weight of thecomposition.

The bulking filler Q2 generally has a particle diameter of greater than0.1 μm, and is selected preferably from ground quartz, zirconias,calcined clays, diatomaceous earths, optionally surface-treated calciumcarbonate, aluminum silicates and/or sodium silicates, aluminas,titanium oxide, and mixtures of these species. On a weight basis, thebulking fillers Q2, when used, are present in the silicone material atfrom 5% to 60% by weight, relative to the total weight of thecomposition X.

The agents which inhibit polyaddition reactions are well-knowncompounds. Use may be made in particular of organic amines, organicoximes, diesters of dicarboxylic acids, acetylenic alcohols, acetylenicketones such as ethynylcyclohexanol, and vinylmethyl-cyclopolysiloxanes(see, for example, U.S. Pat. No. 3,445,420 and U.S. Pat. No. 3,989,667).When present in the composition, the inhibitor is used at from 0.005% to5% by weight, preferably from 0.01 to 3 parts by weight per 100 parts byweight of the polyorganosiloxane V.

The dynamic viscosity of polydimethylsiloxane F which is used as adiluent, at 25° C., is generally between 10 and 5000 mPa·s andpreferably between 20 and 1000 mPa·s.

According to one preferred embodiment, the wetting agent M is asurfactant. Examples of wetting agent M include those from internationalapplication WO-A-2002102326, more particularly the following compounds:

-   -   an ester obtained by esterifying a C₁₃ fatty acid (lauric acid)        with a poly(oxyethylene) glycol containing approximately 9        oxyethylene units, having an HLB of 13.1, sold under the name        Lincol PE 400 ML;    -   a polyethoxylated C₁₃ saturated aliphatic alcohol containing        approximately 8 oxyethylene (OE) units, having an HLB of 12.8,        sold under the name Rhodasurf ROX;    -   a polyalkoxylated C₈ saturated aliphatic alcohol containing a        number of oxyethylene and oxypropylene (OP) units such that the        molecular mass Mw of the polyalkoxylated alcohol is        approximately 1000 g/mol, sold under the name Tegopren LP 111        (abbreviated to TA3);    -   a polyalkoxylated C₁₀-C₁₂ saturated aliphatic alcohol containing        approximately 4 oxyethylene units and 3 oxypropylene units,        having an HLB of 7, sold under the name Antarox FM 33        (abbreviated to TA4);    -   a polyethoxylated C₁₂ saturated aliphatic alcohol containing        approximately 2 oxyethylene units, having an HLB of 8.1, sold        under the name Rhodasurf OT/2.

Other wetting agents M include nonionic, ionic, or amphotericsurfactants. The agents used will be selected as required in a form inwhich they are compatible for contact with the skin and the mucosae,especially the buccal mucosae: they must be nontoxic, nonallergenic andnonirritant at the doses used.

The nonionic surfactants include in particular the following:polyalkoxylated fatty acids; polyalkoxylated alkylphenols;polyalkoxylated fatty alcohols, polyalkoxylated or polyglycerylatedfatty amides; polyalkoxylated fatty amines; polymers resulting from thecondensation of ethylene oxide and/or propylene oxide with ethyleneglycol and/or propylene glycol; polymers resulting from the condensationof ethylene oxide and/or propylene oxide with ethylenediamine;polyalkoxylated terpenic hydrocarbons; polydiorganosiloxanes containingsiloxyl units which carry ethylene oxide chain sequences and/orpropylene oxide chain sequences; polydiorganosiloxanes containingsiloxyl units which carry polyol-type chain sequences; polyalkoxylatedsilanes or polysilanes; alkylglucosides, alkylpolyglucosides; sugarethers; sugar esters; sugar glycerides; sorbitan esters; ethoxylatedcompounds of these sugar derivatives; and mixtures of these surfactants.

The anionic surfactants include in particular: alkylbenzenesulfonates,alkyl sulfates, alkyl ether sulfates, alkylaryl ether sulfates, alkylsuccinates, alkyl carboxylates, alkyl derivatives of proteinhydrolysates, alkyl and/or alkyl ether and/or alkylaryl ether phosphateesters in which the cation is generally an alkali metal oralkaline-earth metal; and mixtures of the aforementioned surfactants.

The cationic surfactants include in particular: trialkylbenzylammoniumhalides; tetraalkylammonium halides; and mixtures of these surfactants.

The amphoteric surfactants include in particular: alkylbetaines,alkyldimethylbetaines, alkylamidopropylbetaines,alkylamidopropyldimethylbetaines, alkyltrimethylsulfobetaines;imidazoline derivatives such as alkylamphoacetates,alkylamphodiacetates, alkylamphopropionates, alkylamphodipropionates;alkylsultaines, alkylamidopropylhydroxysultaines; condensation productsof fatty acids and protein hydrolysates; amphoteric derivatives ofalkylpolyamines; proteins and protein hydrolysates; and mixtures ofthese surfactants.

Specific examples of nonionic surfactants are as follows:

(a) polyalkoxylated C₈-C₂₂ aliphatic alcohols containing from 2 to 25alkoxy units, as for example oxyethylene (OE) and/or oxypropylene (OP)units;(b) polydiorganosiloxanes containing siloxyl units which carry ethyleneoxide chain sequences and/or propylene oxide chain sequences; examplesinclude the surfactants of formulae I, II, and III that are described inU.S. Pat. No. 4,657,959; and(c) mixtures of surfactants (a) with one another, mixtures ofsurfactants (b) with one another, and mixtures of one or moresurfactants (a) with one or more surfactants (b).

The surfactant or surfactants is or are added in an amount of not morethan 10% and preferably not more than 5%, relative to the total weightof the composition X.

For the colorant K, organic and/or inorganic color pigments known in thefield may be used.

With regard to the biocide N which may be employed in the compositionaccording to the invention, it should be noted that this biocide ispreferably selected from the group of active-chlorine precursors basedon N-chlorinated compounds comprising:

-   -   chloramine B (sodium N-chlorobenzenesulfonamide),    -   chloroamine T (sodium N-chloro-p-toluenesulfonamide),    -   dichloroamine T (N,N-dichloro-p-toluenesulfonamide),    -   N-trichloromethylmercapto-4-cyclohexene-1,2-dicarboxylamide,    -   halazone (benzoic acid p-n-dichlorosulfonamide),    -   N-chlorosuccinimide,    -   trichloromelamine,    -   chloroazodine

-   -   N-chloro derivatives of cyanuric acids, preferably        trichloroisocyanuric acid and/or sodium dichloroisocyanuric        dihydrate,    -   N-chlorohydantoins, preferably        1-bromo-3-chloro-5,5′-dimethylhydantoin, or        1,3-dichloro-5,5′-dimethylhydantoin,    -   and mixtures thereof.

This group of antiseptics correspond substantially to the class ofN-chloroamines, which comprises the derivatives of amines in which oneor two of the valences of the trivalent nitrogen are substituted bychlorine. In the presence of water, the N-chloroamines producehypochlorous acid HClO or salts of this acid such as NaClO. HClO andNaClO are active chlorine derivatives which are endowed with a highbactericidal capacity, which can be exploited in the context of theinvention (this is case especially when said material is intended forthe taking of dental impressions in the mouth). At least one differentantiseptic auxiliary may advantageously be associated with antisepticswhich operate by release of chlorine and which are preferably selectedfrom the group of formulations comprising one or more quaternaryammoniums (for example, benzalkonium chloride), and optionally at leastone sequestrating activator, preferably selected from complexing agentsfor metal ions (for example, EDTA or ethylenediaminetetraacetic acid).

The concentration of biocide(s), when used, is not more than 1%,preferably not more than 0.8%, and more preferably still between 0.001%and 0.5% by weight, relative to the total mass of the compositionaccording to the invention.

According to one particular embodiment, a composition X according to theinvention is obtained by mixing the parts A and B in ratios by weight ofbetween 1:10 to 1:1 respectively and preferably by mixing, by weight, 1part of A and 5 parts of B.

According to another particular embodiment the composition X accordingto the invention is characterized in that:

(1) part (A) comprises:

-   -   at least two polyorganosiloxanes V having per molecule at least        two alkenyl groups each bonded to the silicon atom, preferably        vinyl, and having dynamic viscosities ×1 and ×2 at 25° C. in the        ranges 10 to 1000 mPa·s and from 1000 to 150 000 mPa·s        respectively,    -   at least 25% by weight, relative to the total weight of said        part (A), of at least one stabilizer D selected from the group        of starches,    -   a catalytically effective amount of at least one catalyst C        which is a compound of a metal from a platinum group,    -   optionally at least one polyorganosiloxane gum G having per        molecule at least two alkenyl, preferably vinyl, groups which        are bonded to the silicon, and having a viscosity of greater        than 1 000 000 mPa·s at 25° C.,    -   optionally at least one reinforcing filler Q1 and/or one bulking        filler Q2,    -   optionally at least one retarder or inhibitor I of polyaddition        reactions,    -   optionally at least one polydimethylsiloxane F blocked at each        of the chain ends by a trimethylsilyl unit and used as diluent,    -   optionally at least one colorant K,    -   optionally a paraffin P,    -   optionally at least one biocide N,    -   optionally at least one wetting agent M,    -   optionally at least one silicone resin R, and        (2) part B contains no catalyst C and comprises:    -   at least one compound H which is a polyorganosiloxane having per        molecule at least three hydrogen atoms bonded to the silicon,    -   optionally at least one compound V which is a polyorganosiloxane        having per molecule at least two alkenyl, preferably vinyl,        groups bonded to the silicon,    -   optionally at least one stabilizer D selected from the group of        starches,    -   optionally at least one polyorganosiloxane gum G having per        molecule at least two alkenyl, preferably vinyl, groups which        are bonded to the silicon, and having a viscosity of greater        than 1 000 000 mPa·s at 25° C.,    -   optionally at least one reinforcing filler Q1 and/or one bulking        filler Q2,    -   optionally at least one retarder or inhibitor I of polyaddition        reactions,    -   optionally at least one polydimethylsiloxane F blocked at each        of the chain ends by a trimethylsilyl unit and used as diluent,    -   optionally at least one colorant K,    -   optionally a paraffin P,    -   optionally at least one biocide N,    -   optionally at least one wetting agent M imparting a hydrophilic        nature to the surface of said elastomer E or said material M,        and    -   optionally at least one silicone resin R.

According to one advantageous embodiment, the composition X according tothe invention is obtained by mixing parts A and B in weight ratios ofbetween 1:10 to 1:1 respectively, and preferably by mixing, by weight, 1part of A and 5 parts of B.

Another subject of the invention provides a material M or elastomer Eobtained by crosslinking and/or curing the composition X according tothe invention and as defined above.

Lastly, a final subject of the invention relates to the use of thecomposition X according to the invention and as defined above or of thematerial M or elastomer E according to the invention and as definedabove for taking dental impressions, for manufacturing pads employed inpad printing techniques, for producing podiatric orthoses, or for takingan impression of the auditory canal.

This use, in one preferred embodiment, involves ensuring that thecrosslinking of the silicone elastomer is initiated by mixing parts Aand B, reproducing the impression, and allowing crosslinking to continueuntil the elastomer has crosslinked sufficiently and is sufficientlyhard.

According to another mode of use, the material M or elastomer E asdescribed above is intended for the manufacture of pads such as thoseused in pad printing techniques, where it is advantageous to have amaterial that possesses high mechanical properties and has a surfaceenergy that can be modulated by addition of surfactant(s) whileretaining the level of fluidity required for the manufacture of pads bymolding. This other use, in one preferred embodiment, involves ensuringthat the crosslinking of the silicone elastomer is initiated by mixingof parts A and B, forming an object having the shape of the desired padby molding, in a manner known per se, and allowing crosslinking tocontinue until the elastomer has crosslinked sufficiently and issufficiently hard.

Although crosslinking by polyaddition reactions between thepolyorganosiloxanes V and H can be initiated and developed even at atemperature in the region of room temperature (23° C.), crosslinking mayalso be carried out thermally (by heating, for example, at a temperatureof from 60° C. to 110° C.) and/or by electromagnetic radiation(accelerated electronic or “electron beam” radiation) and/or by infraredradiation.

The examples below are given to aid comprehension of the presentinvention, and should not be interpreted as limiting the scope of thepresent invention.

EXAMPLE a) List of Starting Materials Used

-   -   Vinyl polyorganosiloxane V-1: polydimethylsiloxane oil blocked        at each of the chain ends by a siloxyl unit (CH₃)₂(Vi)SiO_(1/2),        with viscosity of 100 000 mPa·s (where Vi=vinyl group).    -   Vinyl polyorganosiloxane V-2: polydimethylsiloxane oil blocked        at each of the chain ends by a siloxyl unit (CH₃)₂(Vi)SiO_(1/2),        with viscosity of 600 mPa·s.    -   Polydimethylsiloxane (PDMS) F-1 blocked at each of the chain        ends by a siloxyl unit (CH₃)₃SiO_(1/2) and having a viscosity of        50 mPa·s.    -   Stabilizer D-1: corn starch.    -   Paste 1: Mixture: vinyl polyorganosiloxane V-2        (polydimethylsiloxane oil blocked at each of the chain ends by a        siloxyl unit (CH₃)₂(Vi)SiO_(1/2), with viscosity of 600 mPa·s)+a        filler Q-1, which is a fumed silica surface-treated with D4        (octamethylcyclotetrasiloxane) in an 85:15 mixture by weight        respectively.    -   Wetting agent M-1: ester obtained by esterifying a C₁₃ fatty        acid (lauric acid) with a poly(oxyethylene) glycol containing        approximately 9 OE units, having an HLB of 13.1, sold under the        name Lincol PE 400 ML®.    -   Catalyst C-1: Platinum.    -   Bulking filler Q2-1: Sicron SA 600: ground quartz with average        particle diameter of 10 mm.    -   Bulking filler Q2-2: Calcium carbonate Calofort-S.    -   Bulking filler Q2-3: zeolite (Zeolite 4 A/S).    -   Colorant K.    -   Hydrogen polyorganosiloxane H-1:        poly(dimethyl)(hydrogenomethyl)siloxane blocked at each of the        chain ends by a siloxyl unit H(CH₃)₂SiO_(1/2), having a        viscosity of 300 mPa·s.

TABLE 1 Formulations of parts A of the two-component systems Components(p/w) Comparative 1 Comparative 2 Comparative 3 Comparative 4Comparative 5 Example 1 Example 2 Example 3 Vinyl polyorganosiloxane V-119.0 19.0 19.0 19.0 19.0 13.8 19.0 19.0 Vinyl polyorganosiloxane V-216.0 16.0 16.0 16.0 16.0 7.0 16 16 PDMS F-1 15.5 15.5 15.5 15.5 15.515.0 15.5 15.5 Stabilizer D-1 22.5 22.5 22.5 0 22.5 34.0 49.5 49.5Bulking filler Q2-2 27.0 27.0 22.0 0 27.0 0 0 0 Bulking filler Q2-1 0 00 39.5 0 5.0 0 0 Bulking filler Q2-3 0 0 5.0 10.0 0 0.0 0 0 Paste 1 0 00 0 0 25.0 0 0 Wetting agent M-1 0 0 0 0 0 0.2 0 0 Catalyst C-1 (ppm)240 375 240 240 253 100 240 240 p/w = parts by weight

TABLE 2 Single formulation for all of the parts B of the two-componentsystems Components (p/w) Amount parts by weight Vinyl polyorganosiloxaneV-1 22.75 Vinyl polyorganosiloxane V-2 4.80 Stabilizer D-1 37.80 Paste 120.00 Wetting agent M-1 0.15 Polyorganosiloxane H-1 4.00 Bulking fillerQ2-1 9.99 Colorant K 0.40

For each two-component system under test, parts A and B, packaged in theform of cartridges, are placed in an oven and undergo accelerating agingat 60° C. After durations of 7 days and 25 days, the properties of theresultant materials are evaluated by crosslinking, at an ambienttemperature at 23° C., a composition obtained by mixing 5 parts byweight of part B with one part by weight of a part A.

Mixing can be carried out either by hand in a beaker or by means of alaboratory metering machine. Evaluation takes place after 7 days and 25days at 60° C. of the following:

-   -   the working time (W.T. in minutes and seconds) of the        compositions resulting from the mixtures of parts A and B as set        out above and in accordance with standard ISO 4823;    -   the elastic memory in accordance with standard ISO 4823; and    -   the Shore A hardness (SAH) after 8 minutes of crosslinking.

After 25 days at 60° C., the presence or absence of blackening of thecartridge containing the catalyst (part A) is ascertained.

The results are set out in table 3.

TABLE 3 Properties measured for each material obtained from the twocomponent systems Properties Comparative 1 Comparative 2 Comparative 3Comparative 4 Comparative 5 Example 1 Example 2 Example 3 W.T. 2′00″1′45″ 1′55″ 2′10″ 2′05″ 1′45″ 1′42″ 1′50″ SAH at t = 0 17.5 25.2 20  17.0 20.5 20.5 21 20 W.T. 1′55″ Not 1′55″ 2′50″ 2′50″ Not 2′00″ 2′05″SAH after 7 days at 60° C. 15.6 measured 19.0 18.5 13.5 measured 18 17W.T./SAH after 25 days Total inhibition; no elastomeric material isobtained 2′10″ 2′15″ 2′30″ at 60° C. 15   15 11 Blackening of thecartridge YES YES YES YES YES NO NO NO containing the catalyst (part A)after 25 days at 60° C.

Comparatives tests 1, 2, 3 and 5 show that even when the stabilizer D ispresent in part A, and at relatively high levels (22.5% by weight,relative to the total weight of part A), this does not preventblackening of the cartridge containing the catalyst (part A) after 25days of storage at 60° C. This is no longer the case for examples 1, 2,and 3 according to the invention, which no longer exhibit this problemof blackening of the parts A comprising the platinum catalyst. Moreover,after aging for 25 days at 60° C. of parts A and B before use, it isobserved that the examples according to the invention produce anelastomer having a working time which is acceptable for use in the fieldof the taking of dental impressions.

1. A method for reducing the blackening phenomena in a composition, themethod comprising: (1) preparing a part A comprising: (a) at least 25%by weight, relative to the total weight of part A, of at least onestabilizer D selected from the group of starches, (b) at least onepolyorganosiloxane V having per molecule at least two alkenyl groups,which are each bonded to a silicon atom, and (c) at least one catalystC, which is a compound of a metal from the platinum group; (2) preparinga part B comprising at least one polyorganosiloxane H having permolecule at least two hydrogen atoms, which are bonded to an identicalor different silicon atom; and (3) mixing part A and part B to form acomposition X; and wherein the composition X is crosslinkable and/orcurable by polyaddition reactions, and takes the form of a two-componentsystem S.
 2. The method as defined by claim 1, wherein the stabilizer Dis present at from 30% to 45% by weight, relative to the total weight ofsaid part A.
 3. The method as defined by claim 1, wherein the at leasttwo alkenyl groups are vinyl groups.
 4. The method as defined by claim1, wherein part A and/or part B comprises at least one compound selectedfrom the group consisting of: a reinforcing filler Q1, a bulking fillerQ2, a retarder or inhibitor I of polyaddition reactions, apolyorganosiloxane gum G having per molecule at least two alkenyl groupswhich are bonded to the silicon, and having a viscosity of greater than1000 Pa·s at 25° C., a polydimethylsiloxane F used as diluent, acolorant K, a plasticizer P selected from the group consisting of liquidpetroleum jelly and a paraffin, a wetting agent M, a silicone resin R,and a biocide N.
 5. The method as defined by claim 4, wherein the atleast two alkenyl groups are vinyl groups.
 6. The method as defined byclaim 4, wherein the wetting agent M is a surfactant.
 7. The method asdefined by claim 1, wherein the stabilizer D is a corn starch.
 8. Themethod as defined by claim 1, wherein the composition X comprises atleast two polyorganosiloxanes V having per molecule at least two alkenylgroups each bonded to a silicon atom, and having dynamic viscosities ×1and ×2 at 25° C. in the ranges 10 to 1000 mPa·s and from 1000 to 150 000mPa·s respectively.
 9. The method as defined by claim 8, wherein the atleast two alkenyl groups are vinyl groups.
 10. The method as defined byclaim 1, wherein parts A and B are mixed in weight ratios of between1:10 to 1:1 respectively.
 11. The method as defined by claim 1, whereinparts A and B are mixed with 1 part of A and 5 parts of B.
 12. Themethod as defined by claim 1, wherein the compound V is apolyorganosiloxane which has per molecule at least two alkenyl groupsbonded to the silicon, comprises: (a) at least two siloxyl units offormula: $\begin{matrix}{T_{a}Z_{b}{SiO}_{\frac{4 - {({a + b})}}{2}}} & (1.1)\end{matrix}$ wherein: the symbols T are identical or different C₂-C₆alkenyl groups, the symbols Z are identical or different monovalenthydrocarbon groups selected from the group consisting of an alkyl having1 to 8 carbon atoms inclusive, optionally substituted by at least onehalogen atom, and an aryl, a is 1 or 2, b is 0, 1, or 2, and the sum a+bis 1, 2, or 3, and (b) optionally at least one siloxyl unit of formula:$\begin{matrix}{{Z_{c}{SiO}_{\frac{4 - c}{2}}};} & (1.2)\end{matrix}$ and wherein: the symbol Z has the same meaning as aboveand c is 0, 1, 2, or
 3. 13. The method as defined by claim 1, wherein:(1) part (A) comprises: at least two polyorganosiloxanes V having permolecule at least two alkenyl groups each bonded to a silicon atom, andhaving dynamic viscosities ×1 and ×2 at 25° C. in the ranges 10 to 1000mPa·s and from 1000 to 150 000 mPa·s respectively, at least 25% byweight, relative to the total weight of said part (A), of at least onestabilizer D selected from the group of starches, a catalyticallyeffective amount of at least one catalyst C which is a compound of ametal from the platinum group, optionally at least onepolyorganosiloxane gum G having per molecule at least two alkenyl,groups which are bonded to the silicon, and having a viscosity ofgreater than 1 000 000 mPa·s at 25° C., optionally at least onereinforcing filler Q1 and/or one bulking filler Q2, optionally at leastone retarder or inhibitor I of polyaddition reactions, optionally atleast one polydimethylsiloxane F blocked at each of the chain ends by atrimethylsilyl unit and used as diluent, optionally at least onecolorant K, optionally a paraffin P, optionally at least one biocide N,optionally at least one wetting agent M, optionally at least onesilicone resin R, and (2) part B comprises no catalyst C and comprises:at least one compound H which is a polyorganosiloxane having permolecule at least three hydrogen atoms bonded to the silicon, optionallyat least one compound V which is a polyorganosiloxane having permolecule at least two alkenyl, groups bonded to the silicon, optionallyat least one stabilizer D selected from the group of starches,optionally at least one polyorganosiloxane gum G having per molecule atleast two alkenyl, groups which are bonded to the silicon, and having aviscosity of greater than 1 000 000 mPa·s at 25° C., optionally at leastone reinforcing filler Q1 and/or one bulking filler Q2, optionally atleast one retarder or inhibitor I of polyaddition reactions, optionallyat least one polydimethylsiloxane F blocked at each of the chain ends bya trimethylsilyl unit and used as diluent, optionally at least onecolorant K, optionally a paraffin P, optionally at least one biocide N,optionally at least one wetting agent M imparting a hydrophilic natureto the surface of said elastomer E or said material M, and optionally atleast one silicone resin R.
 14. The method as defined by claim 13,wherein one or more alkenyl groups present in the composition are vinylgroups.
 15. The method as defined by claim 1, further comprisingcrosslinking and/or curing the composition X to obtain a material M oran elastomer E.
 16. The method as defined by claim 1, further comprisingmaking dental impressions, pads employed in pad printing techniques,podiatric orthoses, or an impression of the auditory canal.